Jeremy Corbyn and Theresa May: one slip-up could affect the outcome of the election.
Composite: PA/Rex

On the evening of the 2 April 2015, you could have cut the tension with a knife in the Thatcher room at Conservative campaign headquarters. That was where we had assembled the “war room”, packed full of Tory spinners and several cabinet ministers for the first TV election debate.

The stakes could not have been higher. We were neck and neck with Labour in polls. And our strategy was coming under fire. Etched in everyone’s mind was the memory of the 2010 election debates, where Nick Clegg had stormed through and arguably cost us an outright majority. A slip-up by David Cameron and history could have been very different.

Monday night’s television appearances by Theresa May and Jeremy Corbyn, where they will each face a grilling from a studio audience and follow-up from Jeremy Paxman, could be just as crucial. But they will not be easy. In carefully choreographed campaigns, election debates pose a huge headache for parties as they try to maintain control of the agenda. Debate preparation by the party leaders can only take you so far. These are the key elements that will decide whether or not the night is deemed a political success by both sides.

Expectation management

Theresa May and her team have got their work cut out. As a clear frontrunner, she has nothing to gain and everything to lose. For the Conservatives, they will want to highlight the fact that expectations are so low for Corbyn, the only way he can go is up. And they will be setting out the key tests for him in areas of perceived weakness – security and the economy. Meanwhile, after the Tories’ difficult week, Labour will want to raise the pressure on the prime minister, framing the night as her first proper “test” as leader.

Ed Miliband and David Cameron clash in the 12015 debate, with Leanne Wood and Nicola Sturgeon. Photograph: Reuters

War room conductor

You cannot run a debate war room by committee and you need one conductor in charge. Calling the shots from the first minute to the last in 2015 for us was Lynton Crosby. With typical bluntness but brutal effectiveness, he set the tone and pace of the Tory response.

Planning your three key moments

Strategically, both media teams will want to split the debate into three parts. First, they will use social media to frame the contest by setting out key questions and tests for the other side. Next, they will try to identify a big flashpoint in the middle of the debate that could be seen as the defining moment. And then they will focus on the aftermath and in particular an attack video of their opponent’s slip-ups to distribute online.

Twitter

Twitter can be an echo chamber, but it is vital. It can shape how the debate is perceived to be going, what the key moments are and what journalists take away. You need to have your army of activists, MPs, ministers and third parties ready to pile in on Twitter before, during and after the debate.

In the 2015 war room, we had a separate screen set up with Tweetdeck monitoring debate hashtags. Jim Messina (Obama’s former campaign chief) had a tool monitoring the volume of tweets between us and Labour minute by minute. When we dipped below Labour, screams of “keep tweeting and retweet” would ring out.

Digital

A good digital team is integral. You need them ready to produce the infographics and videos of the key moments of a debate within minutes to get out to your supporters on Twitter and Facebook – especially vital for hitting a young audience who consume their news online. In the final election debate of 2015, where Cameron and Ed Miliband separately faced a BBC audience, Cameron brandished the infamous note left by Labour’s Liam Byrne after the 2010 election, which said “I’m afraid there’s no money”. We already had our infographics of the letter primed and ready to go the moment he brought it out of his pocket.

The soundbite

Each side will have crafted the 20-second takeaway they want to play out on the TV bulletins.In the seven-way debate in 2015 Cameron gave us our killer soundbite when he pointed down the line of the other six leaders and one by one said “what I’m hearing is more debt and more taxes, more debt and more taxes, a lot more debt and more taxes, some more debt and more taxes, and definitely more debt and more taxes”. Also watch out for the moment when either May or Corbyn stare down the barrel of the camera as they aim to deliver the soundbite that talks directly to people in their living rooms.

Briefing in real time

Ultimately, the debate media war is about momentum and disruption. You need to make sure every journalist covering the debate is getting your single line rebuttals and attacks as it happens. Minute by minute, they will be appearing in email inboxes, on text or WhatsApp. This will be followed by a half time summary and a five bullet-point takeaway at the end.

The spin room

You need to start spinning the outcome before the debate ends and briefing the journalists. And you need to have your big beasts such as Boris Johnson or Peter Mandelson in the spin room giving journalists on very tight deadlines the pithy soundbites that will frame the next day’s headlines.

As May tries to stabilise her lead in the polls, getting through the debates without any slip-ups and neutralising a potential big danger point for the campaign will be seen as a success. Corbyn needs a game changer. TV debates give him the one clear-cut moment to change the conversation.

Giles Kenningham was the Conservative party’s director of communications for the 2015 campaign. Elliot Burton is a former government special adviser. They both work for the public relations firm Trafalgar Strategy.